1. Field of the Invention
The present invention relates to flame retardant ABS resin compositions and more particularly to a ABS rsin compositions incorporating polybrominated higher alkylbenzenes.
2. Description of the Prior Art
Traditionally, most flame retardants, although efficient in their function of retarding the rate of combustion in a resin system, have a tendency to affect adversely one or more key properties of the resin. For example, many flame retardant additives tend to reduce impact strength of the resin; to migrate from the resin composition, resulting in a phenomena known as "bloom"; to volatilize from the resin composition; to plasticize the resin composition adversely, thus lowering the heat deflection temperature, etc.
It is therefore essential that flame retardant agents be specifically tailored to the resin system so that in addition to its role as a flame retardant, the agent will additionally enhance the desirable characteristics of the resin composition. Those skilled in the art well known that the selection of such an application-specific flame retardant is unpredictable at best. Thus, even though a given agent may exhibit utility in a particular resin system, there is no guarantee that this agent will have any use at all with other resins.
Acrylonitrile-butadiene-styrene ("ABS") thermoplastics offer a good balance physical and mechanical properties such as good abuse resistance, heat resistance, moldability, stain resistance, chemical resistance and surface hardness. Because of their properties and their moderate cost, they have been chosen for use in a wide number of applications. For example, they are used by telephone equipment and automotive manufacturers who require materials of high impact strength.
ABS plastics are derived from acrylonitrile, butadiene and styrene. Some of the properties of typical ABS resins are described on pages 1-64, 1-66, and 1-68 of Harper's "Handbook of Plastics and Elastomers", published by McGraw-Hill Book Company in 1975.
A number of flame retardants have been described for ABS resins in the prior art. For example, the following materials have all been used in various ABS systems: bis-(tribromophenoxy) ethane, octabromodiphenyl ether, decabromodiphenyl ether, tetrabromobisphenol-A and its carbonate oligomers, and bis-(pentabromophenoxy)-ethane. Among the prior art specifically dealing with flame retarding ABS resins are U.S. Pat. No. 4,016,139; and U.S. Pat. No. 4,567,218 and references cited therein.
The foregoing flame retardant agents for ABS plastics have not been entirely satisfactory because of problems of "bloom" (also known as thermal migration), heat instability, ultraviolet light instability, discoloration and adverse effects on properties such as impact strength and flowability.
Underwood, et al. U.S. Pat. No. 3,850,882 disclose a three component flame retardant additive mixture for polyolefins, especially polypropylene, consisting of
(a) a halogenated alkyl benzene of the formula ##STR1## where X may be Cl or Br; and Y is a hydrocarbon of 1-20 carbon atoms; a is an integer from 0 to 3; and n is an integer from 3 to 6;
(b) stannic oxide; and
(c) a bis-phenylalkylene hydrocarbon.
The patent does not suggest that such a flame retardant mixture has any utility in ABS resins, let alone that the halogenated alkylbenzene alone would have any such use.
Rueter, et al. U.S. Pat. No. 4,129,551 discloses nonflammable polyester compositions incorporating a phosphorus-containing, multiple component flame retardant additive consisting of:
(a) a triarylphosphine oxide or an aryl or alkyl ester of an arylphosphinic acid;
(b) a nuclear brominated alkylbenzene; and
(c) customary auxiliary agents and additives.
Polyester compositions based on such agents contain 0.5-10% by weight of bromine and 0.1-2% by weight of phosphorus. Among the nuclear brominated alkylbenzenes described were compounds of the following formula: ##STR2## where x=2 to 5; y and z each are zero or an integer from 1 to 17; and sum of y+z is an integer between 7 and 17. Mixtures of such agents are also suggested. There is no disclosure that the additive mixture has any utility in ABS resins or that the nuclear brominated alkylbenzene may be so-used alone for that or any other purpose.
Accordingly, a primary object of this invention is to provide an agent capable of flame retarding ABS resin compositions without exhibiting problems of bloom, heat or light instability, impact strength, or any of the other disadvantages of the prior art ABS flame retardant agents.
A further object is to provide flame retardant ABS resin compositions that exhibit the desired level of flame retardancy without suffering any deterioration of physical properties.
Another object is to utilize polybrominated higher alkylbenzenes as flame retardant agents for ABS resin compositions.